The present invention relates to an electronic fuel injection control apparatus for controlling a quantity of fuel injected from an injector into an internal combustion engine for driving a vehicle.
When an injector(an electromagnetic fuel injection valve), which is mounted on an intake pipe of an engine for example, is used as means for supplying fuel to an internal combustion engine, an injection quantity of the fuel from the injector is controlled by an electronic fuel injection control apparatus (EFI).
Since the injection quantity of the fuel from the injector is required to be determined such that an air-fuel ratio of a mixture supplied to the engine is kept within a predetermined range, it is necessary to estimate an amount of intake air which is sucked into a cylinder during an intake stroke when the fuel injection quantity is determined.
As a method for estimating the amount of intake air which is sucked into the cylinder during the intake stroke of a four-cycle internal combustion engine, a speed-density system has been widely adopted. In the speed-density system which comprises an intake pressure sensor for detecting a pressure at a downstream side of a throttle valve within the intake pipe as an intake pipe pressure (a negative pressure) and speed detecting means for detecting a rotational speed of the engine, the intake air amount is estimated from the intake pipe pressure detected by the intake pressure sensor, the rotational speed of the engine, and an volumetric efficiency of the engine, then the fuel injection quantity to be required is arithmetically operated for obtaining a predetermined air-fuel ratio based on the intake air amount.
The injector opens its valve when a drive current is provided thereto, and injects the fuel provided from a fuel pump into the intake pipe. Generally, a pressure of fuel provided to an injector is kept constantly by a pressure regulator, so that the injection quantity of the fuel from the injector is determined in accordance with a time (a fuel injection time) during which the injector valve is opened. Therefore, in the electronic fuel injection control apparatus, the fuel injection quantity is arithmetically operated as a fuel injection time, then the injector is driven so that the fuel is injected over the arithmetical operation period of time for fuel injection.
FIG. 12, which relates to a four-cycle single cylinder internal combustion engine, shows a change in an intake pipe pressure and a change in an opening degree of the throttle valve relative to a time t when the engine is accelerated, and also shows a change in a fuel injection command signal provided to the injector relative to a time t. In FIG. 12, each of A1 to A4 denotes a period of time during which the engine is on the intake stroke, and Vi1 to Vi4 respectively denote fuel injection command signals provided to an injector drive circuit at a timing ti1 to ti4 of starting the fuel injection during the intake strokes A1 to A4. Width of the injection command signal corresponds to a fuel injection time. The injector drive circuit supplies the drive current to the injector as long as the injection command signals are provided, and then allows the fuel to be injected from the injector.
An actual injector opens its valve to start the fuel injection when the drive current exceeds a predetermined valve opening current value, so that a time width of the injection command signal is not exactly equal to the fuel injection time. However, in this specification, the time width of the injection command signal is taken as the fuel injection time, for the sake of simplicity.
As shown in FIG. 12A, an intake pipe pressure of the four-cycle single cylinder internal combustion engine significantly decreases during the intake stroke, and the intake pipe pressure becomes a minimum at the end of the intake stroke. In an example shown in FIG. 12A, respective minimum values of pressures within the intake pipe during the intake strokes A1 to A4 are P1 to P4, respectively.
In the example shown in FIG. 12, an operation for accelerating the engine is conducted immediately before starting an intake stroke A3, wherein an opening degree of the throttle valve is increased. At a state before conducting the accelerating operation, the opening degree of the throttle valve is kept substantially constant. In this case, minimum values of the intake pipe pressure are substantially constant as represented by P1 and P2, provided that a load does not change. On the contrary, when the accelerating operation is conducted and the opening degree of the throttle valve increases, the intake air amount also increases. Therefore, a minimum value of the intake pipe pressure becomes higher with increase in the opening degree of the throttle valve, as represented by P3 and P4.
FIG. 13, which relates to the four-cycle single cylinder internal combustion engine, shows changes in an intake pipe pressure and in an opening degree of the throttle valve relative to a time t when the engine is decelerated, and also shows a change in a fuel injection command signal provided to the injector relative to a time t. In FIG. 13, each of A1 to A4 denotes a period of time during which the engine is on the intake stroke. And Vi1 to Vi4 respectively denote fuel injection command signals provided to the injector drive circuit at a timing ti1 to ti4 of starting the fuel injection during the intake strokes A1 to A4.
In an example shown in FIG. 13, an operation for decelerating the engine is conducted immediately after completing an intake stroke A2, wherein an opening degree of the throttle valve is decreased. At a state before conducting the decelerating operation, the opening degree of the throttle valve is kept substantially constant. In this case, minimum values of the intake pipe pressure are substantially constant, provided that a load does not change. However, when the decelerating operation is conducted and the opening degree of the throttle valve decreases, the intake air amount also decreases. Therefore, a minimum value of the intake pipe pressure becomes lower with decrease in the opening degree of the throttle valve, as represented by P3, P4, and P5 (an absolute value of the negative pressure will become larger).
In an speed-density type of EFI internal combustion engine, a basic injection time for injecting fuel at each intake stroke is arithmetically operated based on an intake air amount, which has been estimated from an intake pipe pressure and a rotational speed detected during the previous intake stroke, and various control conditions. In a single cylinder internal combustion engine or in a multi-cylinder internal combustion engine which has an intake pipe mounted on each cylinder, wherein an intake pipe pressure has a minimum value, the minimum value detected during the previous intake stroke is used as a value of the intake pipe pressure to be used for estimating the intake air amount.
In an example shown in FIG. 12 for example, a basic injection time for injecting fuel at an intake stroke A2 is arithmetically operated from an intake air amount which has been estimated from a minimum value P1 of an intake pipe pressure and a rotational speed detected during an intake stroke A1. Similarly, basic injection times for injecting fuel at intake strokes A3 and A4 (injection times at a steady operation) respectively are arithmetically operated from respective intake air amounts which have been estimated from minimum values P2 and P3 of pressures within an intake pipe and respective rotational speeds detected during intake strokes A2 and A3. The same is true of an example shown in FIG. 13.
When an opening degree of the throttle valve is maintained substantially constant or when an opening degree of the throttle valve is gradually changed, a difference between an intake air amount during the previous intake stroke which has been used for arithmetically operating the basic injection time and an intake air amount during the present intake stroke does not become larger, so that there is no problem even if the basic injection time arithmetically operated as described above is used as it is as an actual injection time.
However, when an opening degree of the throttle valve is sharply increased when the engine is accelerated, a difference between an intake pipe pressure at a time of arithmetically operating the basic injection time and an intake pipe pressure at a time of actually injecting fuel becomes larger. Therefore, if the basic injection time arithmetically operated as described above is used as it is as the actual injection time, the injected fuel quantity is insufficient and an air-fuel ratio becomes leaner. In an example shown in FIG. 12, a minimum value of an intake pipe pressure during an intake stroke A3 after performing an accelerating operation is extremely larger than a minimum value of an intake pipe pressure during the previous intake stroke A2, hence an intake air amount increases accordingly. Therefore, if an injection time during the intake stroke A3 is arithmetically operated based on the intake air amount which has been estimated from the minimum value of the intake pipe pressure detected during the intake stroke A2, the injected fuel quantity becomes significantly insufficient and an air-fuel ratio becomes leaner.
When the engine enters into its accelerated state, an intake pipe pressure increases and an evaporation rate of fuel decreases, so that a ratio of a fuel deposited on a wall of the intake pipe to a total injected fuel also increases. Therefore, the air-fuel ratio becomes leaner.
It is not preferable that the air-fuel ratio becomes leaner at a time of accelerating the engine, since components of the exhaust gas may deteriorate or running performance may decrease. Thus, in the electronically controlled fuel injection control apparatus which adopts the speed-density system, an increment correction of the fuel injection amount is made at a time of accelerating the engine in order to compensate for a shortfall of fuel.
In an electronic fuel injection control apparatus described in Japanese Patent Examined Application Laid-Open Publication No. 6-25549 for example, a rotational speed of an engine and an opening degree of a throttle valve are detected, an increment correction amount is arithmetically operated based on the rotational speed and the opening degree of the throttle valve, and timing of starting this increment correction is determined from changes in the opening degree of the throttle valve. In this way, the increment correction is made. When it is detected that the intake pipe pressure hardly changes, this increment correction is completed.
In contrast to this, if the throttle valve is abruptly closed at a time of decelerating the engine, an amount of the fuel excessively increases and a air-fuel ratio becomes richer.
For example, when the throttle valve is opened as shown in FIG. 13, a decrease in the intake pipe pressure is small as shown in the intake stroke A1 or A2. However, when the throttle valve is abruptly closed from this opening state, an amount of air amounting into a cylinder of the engine decreases and the intake pipe pressure also decreases. In this Figure, an intake air amount during an intake stroke A4 significantly decreases compared with that during an intake stroke A3, and an intake air amount during an intake stroke A5 further decreases compared with that during the intake stroke A4. Therefore, if the respective injection times during the intake strokes A4 and A5 are arithmetically operated based on intake air amounts which have been estimated from minimum values of the intake pipe pressure detected during the intake strokes A3 and A4 respectively as conducted by the conventional control device, the fuel injection quantity excessively increases and the air-fuel ration becomes leaner.
When the engine enters into its decelerated state, an intake pipe pressure decreases (an absolute value of the negative pressure will become larger) and an evaporation rate of fuel increases, so that almost all fuel injected are evaporated and a portion of the fuel deposited on a wall of the intake pipe is also evaporated. Therefore, the air-fuel ratio becomes richer.
When the air-fuel ratio becomes richer at the time of decelerating the engine as described above, the components of the exhaust gas may deteriorate or running performance may decrease. Thus, in the electronically controlled fuel injection control apparatus which adopts the speed-density system, a decrement correction of the fuel injection quantity is made at a time of decelerating the engine in order to prevent the fuel from being excessively increased.
In a fuel injection control apparatus described in Japanese Patent Examined Application Laid-Open Publication No. 7-13490 for example, the decrement correction is made by detecting from a rate of change of throttle valve opening degree that an operation for decelerating the engine is conducted.
As for the internal combustion engines for driving vehicles, a load on the engine may be abruptly increased and a minimum value of the intake pipe pressure may be raised and further an evaporation rate of the fuel may be decreased due to a clutch control, a steep change in a gradient of road surface, or changes in a condition of road surface, despite the opening degree of the throttle valve being maintained constant. Even when the minimum value of the intake pipe pressure is increased without changing the opening degree of the throttle valves described above, the air-fuel ratio becomes leaner by a synergistic effect of a decrease in the evaporation rate and a delay in the detection of the intake pipe pressure. However, in this case, the increment correction can not be made by a method for correcting the increments of the fuel injection quantity which has been adopted in the conventional electronic fuel injection control apparatus, since the opening degree of the throttle valve is constant.
In an internal combustion engine which employs the electronic fuel injection control apparatus whose rotational speed detected is constant (3000 [r/min.] for example), considering one case where it is detected that a throttle valve opening degree changes by 10xc2x0 from 5xc2x0 to 15xc2x0 and the other case where it is detected that a throttle valve opening degree changes by 10xc2x0 from 50xc2x0 to 60xc2x0, the former requires to be more corrected in order to increase the fuel injection quantity because an accelerating operation has been conducted from its light-load state where a load is hardly applied thereto and consequently an intake pipe pressure largely changes. On the other hand, in the latter case, it is hardly necessary to perform the increment correction because the engine is already in a high-load state at a time of accelerating the engine and an intake pipe pressure is close to an atmospheric pressure.
However, in the conventional apparatus, a correction amount of the fuel injection quantity at a time of accelerating the engine is determined from a rotational speed of the engine and a rate of change of the throttle valve opening degree as described above. Therefore, the increment correction of the fuel injection quantity at the time of accelerating the engine is made by the same amount under the condition that the rotational speed is constant, whether the throttle valve opening degree is changed from 5xc2x0 to 15xc2x0 (a variation amount is +10xc2x0) or the throttle valve opening degree is changed from 50xc2x0 to 60xc2x0 (a variation amount is +10xc2x0). Thus, there has been a problem that an unreasonable control is exercised.
In some conventional electronic fuel injection control apparatus, an increment correction of the fuel injection quantity is made by increasing the respective injection times of a plurality of fuel injections which are continuously performed after the detection of the acceleration state larger than the basic injection time. In this kind of conventional-control apparatus, an injection quantity at a time of the first fuel injection which is performed after detecting its accelerating state is increased, then increments of the fuel is gradually decreased during the plurality of the fuel injections which are performed continuously. Finally, the increments of the fuel become zero.
However, in the above described control, if the throttle valve is operated at a time of accelerating the engine such that an opening degree of the throttle valve is gradually increased at a start of the operation and then is sharply increased from the middle of the operation, the fuel injection quantity can not be increased in response to the sharp increase in the opening degree of the throttle valve. Therefore, the injection amount of fuel may become insufficient and the air-fuel ratio may become leaner.
In the internal combustion engines for driving vehicles, a load on the engine may be abruptly decreased and an intake pipe pressure may also be decreased and further an evaporation rate of the fuel may be increased due to a clutch control, a steep change in a gradient of road surface, changes in a condition of road surface, or slipping of wheels at a time of jumping, despite the opening degree of the throttle valve being maintained constant. In addition to the case where the throttle valve is suddenly closed, even when the intake pipe pressure decreases due to a sharp decrease in the load applied thereto without changing the throttle valve opening degree as described above, the air-fuel ratio becomes richer by a synergistic effect of an increase in the evaporation rate and a delay in the detection of the intake pipe pressure. In this case, the decrement correction of the fuel injection quantity can not be made by a method for correcting the decrements of the fuel injection quantity which has been used for the conventional electronic fuel injection control apparatus, since the opening degree of the throttle valve is constant.
In view of the above described problems, an object of the present invention is to provide an electronic fuel injection control apparatus which allows for prevention of excess and deficiency of an injection quantity caused by a delay in detection of an intake pipe pressure at a time of decelerating and accelerating an engine.
Another object of the present invention is to provide an electronic fuel injection control apparatus which can precisely correct an injection quantity in any of the cases where an engine is accelerated in its light-load state, where an engine is accelerated in its high-load state, and where an engine is abruptly decelerated.
Another object of the present invention is to provide an electronic fuel injection control apparatus which can precisely correct a fuel injection quantity, even when a load applied to an engine is changed under the condition that a throttle valve opening degree is substantially constant.
The present invention is applied to an electronic fuel injection control apparatus, comprising: an injector for injecting fuel into an intake pipe of an internal combustion engine; intake air amount arithmetical operation means for arithmetically operating an intake air amount from an intake pipe pressure of the above described internal combustion engine and a rotational speed of the internal combustion engine; basic injection time arithmetical operation means for arithmetically operating a basic injection time of fuel based on the intake air amount; correction variable arithmetical operation means for arithmetically operating a correction variable which is used for determining an actual injection time by performing a correction operation on the basic injection time; synchronous injection control means for performing an actual injection time processing, in which the actual injection time is arithmetically operated by performing the correction operation using the correction variable arithmetically operated by the correction variable arithmetical operation means at every time a predetermined synchronous injection timing is detected, and for performing a processing in which the synchronous injection is effected by actuating the injector during the arithmetically operated actual injection time.
The present invention comprises: load detecting parameter map storing means for storing a load detecting parameter map which provides a relation among a load detecting parameter which varies depending on a change in a load applied to an internal combustion engine, a throttle valve opening degree of the internal combustion engine, and a rotational speed of the internal combustion engine; map retrieval means for arithmetically operating a map retrieval value on a load detecting parameter map, based on the throttle valve opening degree of the internal combustion engine and the rotational speed of the internal combustion engine, at least at each synchronous injection timing or at the immediately preceding timing; and map retrieval value variation arithmetical operation means in which, at every time the map retrieval value is arithmetically operated by the map retrieval means, the map retrieval value obtained by the map retrieval means at the previous synchronous injection timing or at the immediately preceding timing is used as a comparative reference value and a difference between a map retrieval value newly obtained by the map retrieval means and the comparative reference value is arithmetically operated as a map retrieval value variation.
The above described correction variable arithmetical operation means is comprised such that the correction variable is arithmetically operated relative to the map retrieval value variation when the map retrieval value variation obtained at the synchronous injection timing or the immediately preceding timing exceeds a set value, and the synchronous injection control means is comprised such that the actual injection time processing is performed by using the correction variable obtained by the correction variable arithmetical operation means at the synchronous injection timing or the immediately preceding timing.
The above described correction variable is a variable used for the correction arithmetical operation performed on the basic injection time, and varies depending on the map retrieval value variation which varies depending on a loaded condition of the engine. This correction valuable may be a coefficient by which the basic injection time is multiplied or may be a correction amount which is added to the basic injection time or subtracted from the basic injection time. That is, the correction arithmetical operation performed on the basic injection time for determining the actual injection time may be an arithmetical operation of multiplying the basic injection time by the correction coefficient (the correction variable) or may be an arithmetical operation of adding the correction amount (the correction variable) to the basic injection time or subtracting the correction amount from the basic injection time.
The parameter for detecting the load is a parameter which varies depending on the load applied to the engine, so that the intake pipe pressure, the basic injection time of fuel (the basic injection time), an output torque or the like can be used as this parameter as described below.
The parameter for detecting the load significantly changes when the opening degree of the throttle valve is changed, when the rotational speed is reduced due to an increase in the load on the engine despite the opening degree of the throttle valve being substantially constant, or when the rotational speed is increased due to an decrease in the load on the engine despite the opening degree of the throttle valve being substantially constant. Consequently, the above described retrieval value variation becomes significantly larger when the engine is accelerated or decelerated, or when the rotational speed decreases or increases due to the increase or decrease in the load applied to the engine.
Arithmetically operating the map retrieval value based on the opening degree of the throttle valve and the rotational speed of the engine as described above, a map retrieval value can be obtained which corresponds to a load on the engine predicted from the throttle valve opening degree of the engine and the rotational speed of the engine at a time of the map retrieval. The map retrieval value becomes significantly larger with an increase in the load on the engine when the opening degree of the throttle valve is increased for accelerating the engine or when the load on the engine increases under the condition that the opening degree of the throttle valve is substantially constant (when the rotational speed is reduced despite the opening degree of the throttle valve being constant), for example. On the other hand, the above described map retrieval value becomes smaller when the opening degree of the throttle valve is decreased for decelerating the engine or when the load on the engine decreases under the condition that the opening degree of the throttle valve is substantially constant.
Thus, determining a difference between the map retrieval value and a comparative reference value (a map retrieval value obtained at a timing immediately before the fuel injection which is performed at the previous synchronous injection timing) as a map retrieval value variation as described above, it becomes possible to determine from a sign (positive or negative) of the map retrieval value variation whether the engine is in an acceleration condition or in a deceleration condition, and further, it also becomes possible to precisely detect an loaded condition of the engine in which the fuel injection quantity is requires to be increased or decreased. Therefore, if it is determined whether the fuel should be increased or decreased based on the sign of the map retrieval value variation and also it is detected that the magnitude of the map retrieval value variation exceeds the set value, it becomes possible to precisely determine the correction variable which is used for arithmetically operating the actual injection time consistent with the loaded condition at each moment of the engine, by arithmetically operating the correction variable relative to the map retrieval value variation.
Therefore, in the present invention as described above, the correction variable obtained at each synchronous injection timing or the immediately preceding timing is used as a correction variable which is used for arithmetically operating the actual fuel injection quantity, then the correction arithmetical operation is performed on the basic injection time by using this correction variable in order to determine the actual injection time. The basic injection time in each stroke is arithmetically operated by using an intake air amount which has been estimated based on an intake pipe pressure detected by a sensor during the previous intake stroke. In this way, a fuel injection quantity at each synchronous injection timing is corrected to a proper injection quantity which reflects changes in the loaded condition of the engine estimated at the synchronous injection timing or the immediately preceding timing. Consequently, it is possible to prevent the air-fuel ratio of the gaseous mixture from becoming leaner or richer due to excess and deficiency of the fuel injection quantity caused by the delay in detecting the intake air amount at a time of accelerating or decelerating the engine or at a time of increasing or decreasing the load.
In order to perform the above described control, it is necessary to perform an arithmetical operation for determining the correction variable by the correction variable determination means at the synchronous injection timing or at the immediately preceding timing. To this end, arithmetical operations of the map retrieval value, the map retrieval value variation, and the correction variable may be performed when the synchronous injection timing is detected, for example. Also, the correction variable which has been arithmetically operated at a timing immediately before detecting the synchronous injection timing may be used as a correction variable which is used for arithmetically operating the actual injection time of the synchronous injection by repeatedly performing the arithmetical operations of the map retrieval value, the map retrieval value variation, and the correction variable at very close time intervals (2 msec. intervals, for example).
In the present invention, it is also possible to perform an asynchronous injection such that fuel is injected at any time when it is detected that an injection quantity is insufficient after performing the synchronous injection at a predetermined timing. This asynchronous injection is immediately performed when a deficiency of fuel is detected after the synchronous injection is performed under the condition that a crank angle position is within a range where the fuel injection is permitted.
In the case where the synchronous injection and the asynchronous injection are performed, an electronic fuel injection control apparatus according to the present invention comprises, in addition to load detecting parameter map storing means, map retrieval means, and map retrieval value variation arithmetical operation means which are comprised as described above: asynchronous injection permitting crank angle determination means for determining whether or not a present crank angle position of the internal combustion engine is at a crank angle position where the asynchronous injection is permitted; asynchronous injection time arithmetical operation means for arithmetically operating an asynchronous injection time which is required for making up for a deficiency of fuel when it is detected that the fuel is insufficient after the synchronous injection timing; and asynchronous injection processing means for actuating an injector in order to inject fuel from the injector during the arithmetically operated asynchronous injection time, when the asynchronous injection time arithmetical operation means arithmetically operates the asynchronous injection time after completing the synchronous injection and when it is detected by the asynchronous injection permitting crank angle determination means that the present crank angle position is at a position permitting the asynchronous injection.
In this case, the map retrieval means is comprised such that map retrieval values are arithmetically operated repeatedly at very close time intervals during a time period where the asynchronous injection is permitted at least after completing the synchronous injection and, on the other hand, map retrieval values are arithmetically operated at least at the synchronous injection timing or at the immediately preceding timing during the other time of period. The asynchronous injection time arithmetical operation means is comprised such that the asynchronous injection time is arithmetically operated when it is detected that the map retrieval value variation obtained at the very close time intervals reaches a preset asynchronous determination value. The rest is the same as a case where the asynchronous injection is not performed.
Performing the asynchronous injection at any time when the deficiency of fuel is detected after the synchronous injection as described above, the deficiency of fuel can be immediately made up by the asynchronous injection when the fuel becomes insufficient due to a continuous increase in the opening degree of the throttle valve during a time period where the injected fuel is sucked into a cylinder of the engine after the synchronous injection. Therefore, the air-fuel ratio is prevented from becoming leaner and the running performance of the engine can be improved.
In the electronic fuel injection control apparatus according to the present invention, it is also possible to simultaneously perform the synchronous injection and an additional injection described below in order to prevent the excess and deficiency of fuel which may be caused by a change in the opening degree of the throttle valve and a change in the load after performing the synchronous injection.
The additional injection is performed when the fuel is insufficient at an additional injection timing which is set at a timing immediately before a timing where a time of period for sucking the fuel injected during the intake stroke of the internal engine into the cylinder of the internal combustion engine is completed (at the same timing every time).
In the case where the synchronous injection and the additional injection are performed as described above, the present invention comprises, in addition to load detecting parameter map storing means, map retrieval means, and map retrieval value variation arithmetical operation means which are comprised as described above: additional injection timing detection means for detecting an additional injection timing which has been set at an end of an intake stroke of the internal combustion engine; additional injection time arithmetical operation means for arithmetically operating an additional injection time required for making up for a deficiency of fuel after the beginning of the synchronous injection based on the map retrieval value variation when the latest map retrieval value variation obtained from the map retrieval value variation arithmetical operation means exceeds a preset additional injection determination value; and additional injection processing means for performing processing in order to additionally inject the fuel from an injector during the additional injection time which has been arithmetically operated by the additional injection time arithmetical operation means when the additional injection timing is detected.
In this case, the map retrieval means is comprised such that map retrieval values on the load detecting parameter map are arithmetically operated based on the opening degree of the throttle valve of the internal combustion engine and the rotational speed of the internal combustion engine at least at the synchronous injection timing or the immediately preceding timing and at the additional injection timing or the immediately preceding timing.
The additional injection timing is set at a timing which is before a timing where an intake stroke of the engine is completed such that the additionally injected fuel flows into a cylinder of the internal combustion engine. The rest is the same as a case where the additional injection is not performed.
Preferably, the above described additional injection time arithmetical operation means is comprised such that the additional injection time is arithmetically operated only when the map retrieval value variation exceeds a set value and when the above described rotational speed is less than a set rotational speed and the opening degree of the throttle valve is not less than the additional injection determination value.
Performing the additional injection as described above, the deficiency of fuel, which is caused by continuously opening the throttle valve during a period from the beginning of the synchronous injection to the completion of the intake stroke, can be made up at the last moment of the completion of the intake stroke. Therefore, it becomes possible to prevent the air-fuel ratio from becoming leaner due to the deficiency of fuel at a time of accelerating the engine.
Determining an injection quantity at the additional injection time by estimating a loaded condition of the engine based on a variation of the map value retrieved at the last moment of the completion of the intake stroke relative to a comparative reference value as described above, it becomes possible to inject fuel whose amount is responsive to an air amount which is actually sucked during the intake stroke. Therefore, even when the intake air amount is changed due to the continuous changes in the opening degree of the throttle valve during the intake stroke, it becomes possible to prevent the excess and deficiency of fuel by injecting fuel whose amount is responsive to the actual intake air amount.
The above described load detecting parameter may be a parameter which varies depending on the load condition of the internal combustion engine, and it is preferable that an intake pipe pressure of the internal combustion engine is used as this parameter, for example. In this case, an intake pressure map which provides a relation among the opening degree of the throttle valve, the rotational speed, and the intake pipe pressure of the internal combustion engine is used as a parameter map for detecting the load.
Further, an intake pipe pressure has a minimum value during the intake stroke as in the case of a four-cycle single cylinder internal combustion engine and a multi-cylinder internal combustion engine which has an intake pipe mounted on each cylinder, it is preferable that the minimum value is used as the intake pipe pressure.
Further, the basic injection time of fuel may also be used as the parameter for detecting the load, and the output torque at a time of the steady operation of the engine may also be used as the above described parameter for detecting the load.
When the basic injection time of fuel is used as the parameter for detecting the load, a basic injection time map based on the throttle valve opening degree and speed which provides a relation among the opening degree of the throttle valve, the rotational speed, and the basic injection time is used as the parameter map for detecting the load.
When the output torque of the internal combustion engine is used as the parameter for detecting the load, a torque map which provides a relation among the opening degree of the throttle valve, the rotational speed, and the output torque of the internal combustion engine is used as the parameter map for detecting the load.
The above described correction variable arithmetical operation means is preferably comprised such that the arithmetical operation of the correction variable is performed only when the opening degree of the throttle valve exceeds a predetermined correction permitting throttle opening degree.
According to the construction as described above, it becomes possible to prevent a hunting phenomenon in which an operation for increasing the fuel injection quantity and an operation for decreasing the fuel injection quantity are repeatedly performed.
Also, the above described correction variable arithmetical operation means is preferably comprised such that the arithmetical operation of the correction variable is performed only when a magnitude of the map retrieval value variation exceeds a set value and the rotational speed is less than an increment permitting rotational speed after it is determined from a sign of the map retrieval value variation that the load of the internal combustion engine is changed to be increased, while the arithmetical operation of the correction variable is performed only when a magnitude of the map retrieval value variation exceeds the set value and the rotational speed is not less than an decrement permitting rotational speed after it is determined from a sign of the map retrieval value variation that the load of the internal combustion engine is changed to be decreased.
Further, the above described correction arithmetical operation means is preferably comprised such that the arithmetical operation of the correction variable is performed only when a magnitude of the map retrieval value variation exceeds the set value, the rotational speed is less than the increment permitting rotational speed, and the opening degree of the throttle valve is not less than a predetermined increment permitting opening degree of the throttle valve after it is determined from a sign of the map retrieval value variation that the load of the internal combustion engine is changed to be increased, while the arithmetical operation of the correction variable is performed only when a magnitude of the map retrieval value variation exceeds the set value, the rotational speed is not less than the decrement permitting rotational speed, and the opening degree of the throttle valve is not less than a predetermined decrement permitting opening degree of the throttle valve after it is determined from a sign of the map retrieval value variation that the load of the internal combustion engine is changed to be decreased.